The present invention relates to a golf ball of excellent manufacturability, excellent spin and improved scuff resistance, particularly low-temperature scuff resistance, in which the cover is made using a thermoplastic polyurethane.
Golf balls having a urethane cover are widely used today not only by professional golfers and highly skilled amateurs, but also by beginners and amateur golfers of intermediate skill. Compared with the ionomers commonly used in golf ball covers, urethanes tend to confer golf balls with better spin properties, controllability and low-temperature properties. However, there still remains room for improvement in the low-temperature scuff resistance of these golf balls.
Here, polyurethane materials are broadly divided, based on the process used to make molded articles, into thermoset polyurethane materials and thermoplastic polyurethane materials. Numerous golf balls which use a thermoset polyurethane material have been disclosed in the prior art, including Patent Reference 1: JP-A 2002-272878; Patent Reference 2: U.S. Pat. No. 6,663,510; and Patent Reference 3: U.S. Pat. No. 6,737,498. Patent Reference 1 describes a golf ball which uses as the cover stock a thermoset polyurethane material in which a polycarbonate polyol is employed as the polyol component. Because polycarbonate polyol has excellent heat resistance, weather resistance and water resistance, such golf balls are able to maintain their ball characteristics even under harsh conditions such as rainy weather, extreme heat and scorching sun. However, in the molding of such a thermoset polyurethane material, the heat setting step and the cooling step take a long time. Additional drawbacks include the high reactivity under heating—and thus low stability—of the starting materials, which makes the molding time difficult to control. Thermoset polyurethane materials of this type are thus regarded as having poor productivity when used in the fabrication of specialty moldings such as golf ball covers for enclosing a core.
On the other hand, thermoplastic polyurethane materials are desirable as golf ball cover materials because they can be molded using an injection molding machine, have a short molding time, and are amenable to precision molding. Golf balls using such materials are disclosed in, for example, Patent Reference 4: U.S. Pat. No. 6,739,987 and Patent Reference 5: JP-A 2002-336380. The golf ball described in Patent Reference 4 is a ball composed of a core and a cover, wherein at least the core or cover includes a silicone-urethane copolymer which contains polycarbonate soft segments. The golf ball described in Patent Reference 5 is a golf ball composed of a core enclosed by a cover, the cover being composed primarily of a thermoplastic polyurethane material which contains a polyether polyol having an average molecular weight of at least 1500 and a polyisocyanate, and has a rebound resilience of at least 40%.
However, although the prior art such as above Patent Reference 5 describes a golf ball having both rebound resilience and scuff resistance, there still remains room for improvement in the low-temperature scuff resistance. Hence, a need exists for a way to impart even better low-temperature scuff resistance to golf balls made using thermoplastic polyurethane materials which are injection moldable and provide desirable properties such as excellent ball controllability.